Traffic aware cruise control - should it update the set point?

[Lucky J]

If am driving with the cruise control set to the speed limit, and then the speed limit changes, should the speed set point also change?

For example, i am in a 60mph zone, and the set point has been set to 60mph. The speed limit then changes, let's say to 40mph, should the car change its set point to this new limit or not?

I would have thought so, but that is not what happens for me. The car tells me the new speed limit, and I have to change the set point manually.

 

[spdpsba]

If am driving with the cruise control set to the speed limit, and then the speed limit changes, should the speed set point also change?

For example, i am in a 60mph zone, and the set point has been set to 60mph. The speed limit then changes, let's say to 40mph, should the car change its set point to this new limit or not?

I would have thought so, but that is not what happens for me. The car tells me the new speed limit, and I have to change the set point manually.

The simple answer is, Yes, it does changes to 40 and reduce its speed and that is what I get in my M3.

 

[Lucky J]

The simple answer is, Yes, it does changes to 40 and reduce its speed and that is what I get in my M3.

And does it also adjust for when you are set to 40mph and the limit changes to 60mph?

 

[Dilly]

Yes, it should. However, if you set to the TACC speed limit first and then engage AP, it won’t.
Also, if you engage AP straight off and the limit is say 40, it won’t increase to 60 but will drop to 30 and go back to 40.
If you were to start with a 70 it will drop to any limit and go back as high as 70

 

[Roy B]

It used to do it for me but it doesn't seem to have been doing it recently. Don't know what's changed.

 

[spdpsba]

And does it also adjust for when you are set to 40mph and the limit changes to 60mph?

Yes it does go up according to the sign. This is just TACC and I normally use AP only in motorways where there are not much change in terms of speed limit so didn’t notice what the other user mentioned.

 

[Roy B]

However, if you set to the TACC speed limit first and then engage AP, it won’t.

Can you explain this a little more, I'm not sure I follow.

 

[SpareHeadOne]

The simple answer is, Yes, it does changes to 40 and reduce its speed and that is what I get in my M3.

It's never done that for me, but I have it set to maintain present speed when I engage rather than go to speed limit so I assume that's why.

(I have it set like that because I mostly tend to use it in the average speed section of some major roadworks near me and it ignores the 50 limit.)

 

[UkNorthampton]

" maintain present speed" (or however worded) is my preference - again due to roadworks, temporary limits and avoiding surprise acceleration/deceleration. Then the wind-up/down on right scroll button to set preferred speed or as limits change.

 

[Dilly]

Can you explain this a little more, I'm not sure I follow.

Others may have found that that TACC speeds will change according to speed limits. Mine never has.
if I set TACC during a 60 limit and then engage AP some time after, my speed doesn’t change when a new limit is encountered.
If I go straight into AP, my speed will change as the limits change.

 

[Roy B]

Others may have found that that TACC speeds will change according to speed limits. Mine never has.
if I set TACC during a 60 limit and then engage AP some time after, my speed doesn’t change when a new limit is encountered.
If I go straight into AP, my speed will change as the limits change.

Interesting, thanks.

The other problem is that when you reach a slower speed limit, the car doesn't adjust until it is past the sign, which means I'll have manually reduced it before then, anyway. If, as other people are suggesting, it will never raise the speed above the manually set speed, then that explains why it never reacts to the increased limit for me, since I will almost always have manually reduced the speed to the lower limit.

That, plus the fact that it can't recognise variable speed limits or temporary speed restrictions on motorways anyway.

 

[Dilly]

Interesting, thanks.

The other problem is that when you reach a slower speed limit, the car doesn't adjust until it is past the sign, which means I'll have manually reduced it before then, anyway. If, as other people are suggesting, it will never raise the speed above the manually set speed, then that explains why it never reacts to the increased limit for me, since I will almost always have manually reduced the speed to the lower limit.

That, plus the fact that it can't recognise variable speed limits or temporary speed restrictions on motorways anyway.

Yes that sums it up

 

[DGSteig]

Others may have found that that TACC speeds will change according to speed limits. Mine never has.
if I set TACC during a 60 limit and then engage AP some time after, my speed doesn’t change when a new limit is encountered.
If I go straight into AP, my speed will change as the limits change.

I have been wondering why my M3 changes speed limits somewhat randomly. Most of the time it doesn't, so when it does it confuses me. I will test this theory, I usually use only TACC, so if I understand you TACC doesn't change speed according to the speed limit. I have seen it respond to other signals, for instance it often seems to slow down dramatically in work zones where there are no speed limit signs, sometimes indicating the speed change on the display and other times just slowing down. Anyone seen that? Sometimes I think it is confused thinking I am on an access road. Once I am passed the weird zone it will resume the previous set speed. That is why I always drive with my foot resting lightly on the pedal, so I can override quickly.

 

[DGSteig]

I have been wondering why my M3 changes speed limits somewhat randomly. Most of the time it doesn't, so when it does it confuses me. I will test this theory, I usually use only TACC, so if I understand you TACC doesn't change speed according to the speed limit. I have seen it respond to other signals, for instance it often seems to slow down dramatically in work zones where there are no speed limit signs, sometimes indicating the speed change on the display and other times just slowing down. Anyone seen that? Sometimes I think it is confused thinking I am on an access road. Once I am passed the weird zone it will resume the previous set speed. That is why I always drive with my foot resting lightly on the pedal, so I can override quickly.

Actually, I just drove back from Myrtle Beach (good timing!) and I used AutoPilot almost continuously. I only noticed it changing the speed limit a couple of times, but maybe that is because I fiddled with the speed limit not infrequently. I will make a more formal test.

 

[Tony Hoyle]

It's extremely inconsistent. I've had two teslas now and have never seen speeds change as a result of a limit change, except on one 30mph road near me that you'd be nuts to use TACC/AP on anyway.. My working theory is it's only enabled for certain roads and I don't live near any of them.

Which IMO is a good thing as speed limits are all over the place.. I really don't want the car to suddenly decide it's in a 20mph zone on the motorway. I did hope they'd implement it for average speed zones now it's supposed to recognise them (and indeed did appear to last time I went through them ) but the AP set speed remained at 70).

Random slowing down, yeah.. but that isn't a change in the set speed it's just AP randomness. Sometimes confused with phantom braking (but it feels far more deliberate).